Dilute operation of internal combustion engines through lean fueling and/or high levels of exhaust gas recirculation (EGR) is frequently employed to increase fuel efficiency and reduce emissions. In particular, for spark-ignition engines, dilute operation is a promising approach for increasing engine efficiency, in the form of either lean burn (air dilution) or EGR (inert dilution).
In the case of spark-ignition engines, primary limitations of dilute combustion are due to poor flame speed and flame growth instability. Various methods have been developed to reduce these limitations, such as enhanced ignition systems and charge motion improvements. Intake charge composition modifications, either through fuel reforming for lean dilution applications or exhaust reforming for EGR applications, has also been shown to improve dilute combustion by improving thermal efficiency.